Sight

Abstract: The invention relates to a sight having a day-sight part (3) and a night-sight part (2). By means of quenching the visible light with a filter, the night-sight part in the form of an IR sight can be used during the daytime as well. In order to effect an improved use of the night sight under daylight conditions, a filter (11) with a filter characteristic which quenches visible light having wavelengths outside the wavelengths of blue light is arranged, according to the invention, in the beam path for the incoming visible light.

Description: The present invention relates to a sight comprising an IR camera which converts thermal radiation which is coming in towards the opening of the IR camera into a red visible image, a sight part for incoming visible light, and means for guiding the image generated by the IR camera into the beam path for the incoming visible light so that the visible image generated by the IR camera and the image corresponding to the incoming visible light are superimposed and can be viewed simultaneously. By means of supplementing the sight part for incoming visible light, the so-called day sight, with an IR camera, a sight is obtained which can also be used in the dark and in bad weather, a so-called night sight. The invisible thermal radiation from the terrain is converted into an image which is visible to the eye. The image is reflected into the day sight using a beam splitter. Under normal conditions of daylight, the day-sight image is many times brighter than the image coming from the night sight and therefore completely dominates the image of the terrain which an observer sees. Under certain circumstances, however, it is of interest to be able to use the IR sight during daytime as well. In order to achieve this, it is known to introduce a filter, which in principle excludes all daylight, into the beam path for incoming visible light. When such a filter is present in the beam path, information about the terrain is obtained solely in the IR range. Examples of prior art sights are disclosed in US 5035422 and US 5129309. According to US 5035422 the incoming light is divided into three different spectra, namely a visible spectrum, a near infrared spectrum and a far infrared spectrum. In one mode the near infrared spectrum and the far infrared spectrum may be activated simultaneously. There is no mode proposed to activate the visible spectrum simultaneously with another spectrum and accordingly no measures proposed to carry out such an activation. According to US 5129309 the daylight image is combined with an aiming mark. There is no simultaneously combining with other spectra proposed. It is to be noted that the sight according to US 5129309 also is equipped with a video observation system involving video and IR cameras. Infrared blocking and infrared enhancing filters are to be used in connection to these cameras. The object of the present invention is to effect improved use of the night sight under daylight conditions. This is achieved by means of a sight which is characterized in that a filter with a filter characteristic which quenches visible light having wavelengths outside the wavelengths of blue light is arranged to be introduced into the beam path for the incoming visible light in a position before the superimposition of the visible image generated by the IR camera and the image corresponding to the incoming visible light to make the red image which is faint visible at the same time as a brighter image of the incoming visible light. A filter with the filter characteristic in accordance with the preceding paragraph, which filter is termed " blue filter" in that which follows, quenches all visible light apart from blue light. When this filter is inserted into the beam path, the faint red image of the terrain which has been reflected in from the night sight is now also visible. There are many advantages in introducing a blue filter. Due to the fact that the day-sight image is still visible, even thought with a strong blue tinge, a more detailed image of the surroundings is obtained, thereby facilitating the user's orientation in the terrain. At the same time, the superimposed IR image shows where warm objects, which can be of interest to the user, are present in the terrain (" hot-spot detection" ). The day image facilitates identification of an object. Objects which are hidden behind vegetation, for example, are also revealed by the IR image. The effect is further are also revealed by the IR image. The effect is further intensified in the eye by means of the colour contrast blue/red in the image containing a blue day-light image and a red IR image. According to an advantageous embodiment, the filter consists of BG glass, such as BG-1, which has been found to have quenching properties within the wavelength range for visible light which are suitable in this context. The fact that the blue light is also quenched somewhat does not prevent the filter from being designed so that a blue image of the terrain is visible in the day sight. According to another advantageous embodiment, the filter can be introduced pivotably into the beam path, and according to a further advantageous, alternative embodiment can be introduced displaceable into the beam path. The latter two embodiments permit the observer to switch the filter in the sight, in a simple manner, between, on the one hand, day-sight function only and, on the other hand, a function combining IR sight and day sight for daylight conditions. The invention will be described below in more detail with reference to the attached drawings in which Figure 1 shows a first diagrammatic embodiment, in partially sectioned view, of a sight according to the invention having a filter which can be introduced pivotably, and Figure 2 shows a second diagrammatic embodiment, in partially sectioned view, of a sight according to the invention having a filter which can be introduced displaceably. The sight 1 which is shown comprises, in accordance with the embodiments shown in Figures 1 and 2 and IR camera 2, a sight part 3 for visible light and a connecting part 4 which couples the IR camera 2 and the sight part 3 together optically. In the IR camera, the invisible thermal radiation from the terrain which passes through the opening 8 of the camera is converted to a visible image. The image is generated by red light-emitting diodes (not shown) operating in a wavelength range around 650 nm. the IR camera operates with a magnification of 1 : 1, signifying that the converted IR image and the ordinary day image are of the same size. The image from the IR camera 2 is reflected into the sight part 3 by means of a number of optical components arranged in the connecting part 4. A beam splitter 6, preferably of the dichroic type, is included as an essential component in the connecting part 4. A plane mirror 7 reflects the converted IR image in towards the beam splitter 6 which, within the frequency range of the converted IR image, reflects the IR image towards the sight part 3. Visible light coming in towards the sight part 3 reaches, via an opening 9, the beam splitter 6, which transmits the light towards the sight part 3. The sight part 3 consists of a conventional day sight and will not be described in more detail here. Two filters 10, 11 are arranged in association with the opening 9 of the connecting part 4. In accordance with Figure 1, these two filters are arranged pivotably around an axle 12 in front of the opening 9 of the connecting part. The filter 10, shown in the raised position, is of the type which it is known to introduce into the beam path in order to quench daylight when using the IR sight during the daytime. The filter 11, shown in the lowered position, consists of a blue filter having the property of essentially transmitting blue light but suppressing remaining visible light. Three operational situations can be distinguished. When both the filters are in the raised position, the observer 14 is presented with a conventional day image. When both the filters are in the lowered position, visible light is screened off and the observer 14 is presented solely with an IR image. When the filter 10 is raised and the filter 11 is lowered, a blue day-sight image is obtained which has a red night-sight image reflected into it. In accordance with the embodiment shown in Figure 2, the two filters 10, 11 can be introduced displaceably in front of the opening 9 of the connecting part. Guide rails 13 limit the movements of the filters. As was the case with the embodiment according to Figure 1, the observer 14 can be presented with three different image types. The embodiment in accordance with Figure 2 also permits the sequence of the filters in the beam path to be changed. As is indicated by the dashed lines 15 in Figure 2, the blue filter can consist of several filter elements which can be introduced separately in front of the opening 9 of the connecting part 4. Such an arrangement increases the possibilities of varying the blue-filter quenching. In this context, each filter element which is included can be entirely responsible for the blue-filter quenching, or else a number of blue filter elements can be combined.

Claims: Sight comprising an IR camera (2) which converts thermal radiation which is coming in towards the opening of the IR camera into a red visible image, a sight part (3) for incoming visible light, and means (4) for guiding the image generated by the IR camera into the beam path for the incoming visible light so that the visible image generated by the IR camera (2) and the image corresponding to the incoming visible light are superimposed and can be viewed simultaneously, characterized in that a filter (11) with a filter characteristic which quenches visible light having wavelengths outside the wavelengths of blue light is arranged to be introduced into the beam path for the incoming visible light in a position before the superimposition of the visible image generated by the IR camera and the image corresponding to the incoming visible light to make the red image which is faint visible at the same time as a brighter image of the incoming visible light. Sight according to the preceding claim, characterized in that the filter (11) consists of so-called BG glass, such as BG-1. Sight according to either of the preceding claims, characterized in that the filter (11) exhibits a filter characteristic having a first quenching level within the wavelength range for blue light and a second quenching level, which is much higher in relation to the first quenching level, for visible light outside the wavelengths of blue light. Sight according to any one of the preceding claims, characterized in that the visible image generated by the IR camera (2) is generated by light-emitting diodes having a wavelength around 650 nm. Sight according to any one of the preceding claims, characterized in that the filter (11) can be introduced pivotably into the beam path. Sight according to any one of Claims 1-4, characterized in that the filter (11) can be introduced displaceably into the beam path. Sight according to any one of the preceding claims, characterized in that the filter (11) consists of a number of filter elements (15) which can be introduced into the beam path for the incoming visible light.

Inventors: JOHANSSON STEFAN, SANDSTROEM UNTO, JOHANSSON, STEFAN, SANDSTROEM, UNTO, Sandström, Unto
Applicants: CELSIUSTECH ELECTRONICS AB
Application year: 1994
Main classification: G02B23
IPC codes: G02B23